The present invention relates to a hydraulically controllable globe valve, in particular a gas exchange valve of an internal combustion engine, having a stem piston to which a pressure can be applied by hydraulic spring means connected to a pressure source, and which can move from one end position in the direction of a second end position.
A hydraulic actuator for a globe valve in an internal combustion engine, which is known from German Patent No. 38 36 725, has a piston connected to the valve shaft and guided in a cylindrical working space, with a spring-loaded arrangement provided at both ends of the piston so that the piston is forced, when rest, into a central position in which the globe valve is partially open. To move the globe valve into an open or closed position, hydraulic pressure can be alternately applied to the piston from a pressure source. A feed pump serving as the pressure source and a switchable multiway valve are provided for this purpose.
A hydraulic valve controller for a globe valve in an internal combustion engine, which is known from German Patent No. 195 01 495, has a helical compression spring that loads the globe valve in the closing direction as well as hydraulic spring means that can be connected alternately to a pressure source and a pressure sink by a switchable multi-way valve, with these spring means being able to move the globe valve in the opening direction via a stem piston that can move along with the globe valve.
Hydraulic control mechanisms for a gas exchange globe valve in an internal combustion engine are known from German Patent No. 196 21 951 and German Patent No. 196 21 719, in which first spring means loading the valve in the closing direction and second spring means loading the valve in the opening direction via a stem piston are assigned to the globe valve, with these spring means including a series arrangement of one mechanical and one hydraulic spring. The second spring means form a spring arrangement with a progressive total spring characteristic, with the hydraulic spring being prestressed by a force exceeding the maximum force of the helical spring as a function of the opening work of the globe valve. A correspondingly high supply pressure for the control mechanism is provided for this purpose.
A hydraulic control mechanism for a globe valve in an internal combustion engine, to which there are assigned first spring means for applying pressure in the closing direction and second hydraulically controllable spring means for applying pressure in the opening direction, is known from German Patent No. 197 16 042. The second hydraulically controllable spring means can be cyclically applied with pressure and then relieved again, with an auxiliary control element, which can relieve the pressure on the second hydraulically controllable spring means in the event of a globe valve malfunction, being assigned to these second hydraulically controllable spring means. The auxiliary control element preferably has a 2/2-way valve function and is connected via control lines to a pressure supply line and a pressure relief line which can be switched by a central actuator having an on-off valve. The auxiliary control element is also held in its closed rest position by a mechanical resetting spring.
As mentioned above, the fact that the actuating energy, e.g., the opening energy, of a exhaust valve fluctuates with the combustion chamber pressure, and thus with the engine load, is a problem in gas exchange valves of internal combustion engines. The conventional remedy is to set different opening forces, which can be done using the above-mentioned spring means having a series arrangement of one mechanical and one hydraulic spring. One drawback of this arrangement, however, is that the working space volume of the hydraulic spring increases as the opening movement of the valve stem piston begins, causing the hydraulic pressure built up at the spring to drop rapidly. In addition, the hydraulic pressure setting of the hydraulic spring must be adjusted to the engine operating state to generate an optimum force for opening the valve.
An object of the present invention is to provide a globe valve of the type mentioned in the preamble which can be moved by a variable actuating energy supplied by the hydraulic spring means without requiring any variable supply pressures for the hydraulic spring means.
This object is achieved according to the present invention by providing pressure control means which maintain a constant pressure of the hydraulic spring means on the stem piston while the latter moves from the first end position in the direction of the second end position by connecting the hydraulic spring means to the pressure source during a variable portion of the valve lift. This makes it possible to vary the energy applied to the stem piston during the valve lift by selecting a longer or shorter value for the portion of the valve lift during which the hydraulic spring means apply the working pressure of the pressure source to the stem piston, at the same time maintaining a constant hydraulic spring means pressure. As a result, the actuating energy of the globe valve can be varied without changing the working pressure of the pressure source.
In one embodiment of the present invention, the hydraulic spring means are connected to the pressure source by the fact that the pressure control means is provided with a first annular space connected to the pressure source and located in a valve housing surrounding the stem piston as well as a further annular space connected to the hydraulic spring means via a pressure channel, with this second annular space being connected to the first annular space via a control groove in the stem piston during the variable portion of the valve lift. This automatically connects the hydraulic spring means to the pressure source when the stem piston moves from the first end position in the direction of the second end position, provided that the first annular space is connected to the pressure source. The hydraulic spring means are also automatically separated from the pressure source as soon as the control groove no longer connects the two annular spaces to each other. As long as the two annular spaces are connected via the control groove, the application of supply pressure from the pressure source to the hydraulic spring means can be controlled by opening and closing the connection between the first annular space and the pressure source.
In a further embodiment of the present invention, the hydraulic spring means are connected to the pressure source by providing the pressure control means with a first annular space connected to the pressure source and located in a valve housing surrounding the stem piston as well as a control groove, located in the stem piston, which can be connected to the hydraulic spring means via a pressure channel provided in the stem piston, with the control groove being connected to the annular space during the variable portion of the valve lift. This automatically connects the hydraulic spring means to the pressure source while the step piston moves from the first end position in the direction of the second end position, provided that the first annular space is connected to the pressure source. The pressure channel to the hydraulic spring means is arranged in an especially simple and space-saving manner within the stem piston. The hydraulic spring means are disconnected from the pressure source as soon as the control groove is no longer connected to the first annular space. As long as the control groove is connected to the first annular space, the application of supply pressure from the pressure source to the hydraulic spring means can be controlled by opening and closing the connection between the first annular space and the pressure source.
In a further embodiment of the present invention, the pressure channel contains a non-return valve which prevents the pressure in the hydraulic spring means from decreasing via the pressure channel. When the pressure channel is connected to the pressure source, the non-return valve opens as the pressure in the hydraulic spring means drops below the supply pressure of the pressure source following a movement of the stem piston.
In a further embodiment of the present invention, the first annular space can be connected to the pressure source via a hydraulic actuator that also causes the stem piston to move from a first end position in the direction of a second end position. This eliminates the need to provide a separate actuator for the pressure control means. The beginning of the variable portion of the valve lift is defined by the connection between the control groove in the stem piston and the first annular space. The end of the variable portion of the valve lift is defined either by separating the control groove from the first annular space or switching the hydraulic actuator.
In a further embodiment of the present invention, the pressure control means for connecting the hydraulic spring means to the pressure source have a shutoff element for closing the pressure channel, with the shutoff element being alternately connected to the pressure source and a pressure sink through hydraulic means for opening and closing the pressure channel at a first end and being held open during the variable portion of the valve lift. The shutoff element can be controlled independently of the pressure in the pressure channel through hydraulic means. Using the shutoff element eliminates the need for a hydraulic medium flowing to the hydraulic spring means to pass through an on-off valve with an adequately large opening cross-section.
In a further embodiment of the present invention, the shutoff element for closing the pressure channel is assigned a resetting spring that operates in the closing direction of the shutoff element, and the shutoff element is connected to the hydraulic spring means in a way that allows pressure to be applied, opening the pressure channel against the force of the resetting spring. This allows the shutoff element to open and close as a function of the difference between the pressure in the hydraulic spring means and the control line pressure.
In a further embodiment of the present invention, the control line can be connected to the pressure source and the pressure sink via a hydraulic actuator that also triggers the movement of the stem piston from the first end position in the direction of the second end position. The hydraulic actuator thus controls both the stem piston and the shutoff element. In an alternative embodiment of the present invention, the control line is connected to the pressure source via a throttle and to the pressure sink via an on-off valve. The control line is preferably coupled with the pressure source and pressure sink so that the shutoff element also opens when the stem piston moves from its first end position, in which the valve is closed, in the opening direction.
In a further embodiment of the present invention, the pressure control means define the variable portion of the valve lift, and thus the valve actuating energy, as a function of a counter-pressure acting upon the valve, in particular as a function of the combustion chamber pressure and thus the engine load in the case of a gas exchange valve of an internal combustion engine.